The present invention relates to novel interconnected cell activated reticulated or unreticulated carbon structures having a uniquely high combination of compressive strength and of activated surface area per unit mass and volume. In particular, the present invention relates to such carbon structures derived by carbonization from an alloy of a polyurethane resin and a furan resin in the form of a foam structure with membranes or a skeletal structure without membranes.
Activated carbon is well known and is carbon which has been activated by oxidation. The activation process usually destroys some of the carbon to provide a channeled mass which adsorbs chemicals from solution or from a gas. The surface area per unit mass or volume is a measure of the ability of the activated carbon to adsorb various chemicals. The level of such activation is highly unpredictable and depends upon the parent carbonizable structure from which it was derived and the specific process of activation. Because the process is destructive, the carbon structure physical strength is reduced as the level of activation is increased.
U.S. Pat. No. 2,365,729 (1944) to Schumacher et al describes catalytic activated carbon particles prepared by heating in the presence of an oxygen containing oxidizing agent, such as heating in air at between about 200.degree. C. and 450.degree. C., and then a subsequent special heat treatment in the absence of air or other oxidizing media at a critical temperature of 925.degree. C. to 1000.degree. C. The activated carbons so produced are disclosed to function as catalysts in the oxidation of inorganic compounds such as ferrous iron to ferric iron. It would be desirable to have a unitary, strong porous structure with this property.
U.S. Pat. No. 3,778,387 (1973) to Urbanic et al describes air oxidized activated carbon particles which are rendered antioxident by treatment of the activated carbon particles with a ketone which is adsorbed on the particles but which does not interfere with the adsorption of other compounds. The activation of the carbon particles is at a temperature of 100.degree. C. to 600.degree. C. Again it would be desirable to provide a unitary strong structure of this kind as well.
U.S. Pat. No. 3,917,806 (1975) to Amagi et al describes a porous carbon molding, which is derived from a porous pitch by carbonization in contact with an oxidizing agent, such as steam vapor at 850.degree. C. for 8 hours or such as air. The porous carbon structures have activated surface areas of around 1,100 square meters per gram. These porous carbons from pitch are likely to exhibit a variance in the activity and cell size from batch to batch and even within portions of the sample, and have a relatively high bulk density of about 1.7 gm/cc as shown in Examples 6 and 7 of the patent.
U.S. Pat. No. 3,960,761 (1976) to Burger et al describes forming molded beads of carbon particles and thermosetting resin binder which are activated by heating with steam or with carbon dioxide as the oxidizing agent. The binder is a phenolic fusible or thermosetting resin and the activation temperatures are between 700.degree. C. to 1200.degree. C. The carbon structures are substantially non-porous and as a result have high compressive strengths.
U.S. Pat. No. 4,029,600 to Schmitt et al (1977) describes the use of various oxidizing agents, such as oxygen, carbon dioxide, steam and the like for activating carbon particles which are to be bonded. The carbon structures are made of spherical activated carbon particles bonded with a carbonizable binder and then heated at 600.degree. C. in a non-reactive atmosphere. The resulting activated carbon products have relatively low compressive strengths and activated surface areas ranging up to about 1300 square meters per gram. Bound oxygen on the surface of the activated carbon is disclosed to render the surface more adsorbent to polar compounds and less adsorbent to non-polar compounds.
U.S. Pat. No. 3,922,334 to Marek et al (1975) describes reticulate carbon skeletal structures which are similar in geometry to those of the present invention. These skeletal structures are formed by infusing a polyurethane resin reticulate structure with a phenolic resin dissolved in a solvent and then carbonizing the infused structure. The infused or the carbonized reticulate structures are activated with an oxidizing agent at around 825.degree. C. to 900.degree. C. As can be seen from Table IV of this patent, the activated structures have a maximum activated surface area of 1416 square meters per gram and have low compressive strengths for the most active structures. There is also a very large activation weight loss for the most active structures and the resulting structures are so fragile that they break merely as a result of handling. The Marek activated carbon reticulate structure geometry is nevertheless very desirable; however, because of the inherently destructive nature of oxidation of the carbon skeletal structures to achieve satisfactory activation the resulting structures were of necessity very fragile.